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FUSARIUM WILT OF POTATO IN THE HUDSON 
RIVER VALLEY, NEW YORK 



BY 



ROYAL J. HASKELL 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 

OF CORNELL UNIVERSITY FOR THE DEGREE 

OF DOCTOR OF PHILOSOPHY 



Reprinted from Phytopathology, Vol. IX, No. 6 
June, 1919 




FUSARIUM WILT OF POTATO IN THE HUDSON 
RIVER VALLEY, NEW YORK 



BY 

ROYAL J. HASKELL 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 

OF CORNELL UNIVERSITY FOR THE DEGREE 

OF DOCTOR OF PHILOSOPHY 



Reprinted from Phytopathology, Vol. IX, No 6 
June, 1919 



-^ 



<$& 



\ 



Reprinted from Phytopathology, Vol. IX, No. 6, June, 1919 



FUSARIUM WILT OF POTATO IN THE HUDSON RIVER VALLEY, 

NEW YORK 1 

Royal J. Haskell 

With Plates XIII to XV 

During the summer of 1914 a disease of potatoes resembling Fusarium 
wilt was reported as being serious in various parts of the southern Hud- 
son River Valley, particularly in Dutchess County, N. Y. The effect 
of this disease on the tops of the plants was the same as that described 
by Smith and Swingle (14), Manns (6), Orton (9, 10), and others as 
being due to Fusarium oxysyorum. The condition of the affected tubers, 
however, was somewhat different from that commonly reported for Fu- 
sarium wilt. Because of the seriousness and somewhat doubtful identity 
of the trouble it was deemed advisable to make a closer study of the dis- 
ease. The following paper gives the results of work during the years of 
1915 and 1916, the summers being spent in a field laboratory in Dutchess 
County, and the winters at the College of Agriculture at Ithaca, N. Y. 

The Host 

potato production in the lower hudson river valley 

Potato raising in the southern portion of the Hudson Valley occupies 
a relatively small place on the average farm. Indeed, so few potatoes 
are produced that there are not enough to supply the local markets and 

1 Also presented to the Faculty of the Graduate School of Cornell University, 
July, 1917, as a major thesis in partial fulfillment of the requirements for the de- 
gree of doctor of philosophy. 

The writer wishes to acknowledge the valuable aid of Professor M. F. Barrus 
under whose supervision this investigation was conducted. Thanks are also due 
the Dutchess County Farm Bureau Association and Mr. Henry Morgenthau, Jr. 
for financial assistance in connection with the work. 



224 Phytopathology [Vol. 9 

importation from outside sources is necessary. This condition has not 
always existed, however, as fifty or sixty years ago potatoes occupied an 
important place among the farm crops. The census figures show that 
in 1839 Dutchess County produced 590,000 bushels and in 1849, 385,941 
bushels, while in 1899 and 1909 only 210,437 and 300,275 bushels re- 
spectively were reported. This decrease in production is partly due to 
lower yields and partly to fewer acres being planted. The following 
figures show the general decrease in number of acres devoted to potatoes 
in the county during the last forty years; in 1879, 4218 acres, in 1889, 2941 
acres, in 1899, 2693 acres, in 1909, 3041 acres. Furthermore it is the 
opinion of many of the older inhabitants of this section that potatoes 
do not produce so well as they did fifty years ago. As a result of the 
lower yield it has gradually been concluded that potatoes are not a prof- 
itable crop in Dutchess County and the acreage has slowly fallen off. 

Much of the soil, of which there are many types, is well adapted to 
potato culture but the climate is not favorable to the crop on account 
of the high summer temperatures which prevail throughout the months 
of July and August. Potatoes are planted in May or June and as a 
result they are often at the height of their growth when they encounter 
hot weather and drought. Under these conditions the vines tip-burn, 
become subject to Fusarium wilt and die early with a yield which is far 
below the average per acre of the state. This holds true, not only for 
Dutchess County, but for the entire southern Hudson River Valley where 
much the same climatic and soil conditions exist. 

With the exception of several fields of twenty to forty acres the in- 
dividual potato fields in Dutchess County are of small size. The yield 
is rather light, being as a rule from ten to twenty-five bushels lower than 
the average for the state. Most of the potatoes planted in this locality 
are late varieties of both the Green Mountain and Rural groups, although 
some farmers grow for home use a few early potatoes such as the Early 
Rose and Irish Cobbler. Much of the seed is obtained through local 
dealers who buy from Maine or western New York. It is generally 
considered in Dutchess County that homegrown potatoes do not give 
good results when planted year after year and as a result we find farmers 
frequently changing their seed. 

Potatoes are commonly planted on sod or after corn and often the 
same piece of land is used for the crop two or more successive years. Ma- 
nure and commercial fertilizer are used either separately or together. 
The crop is cared for mostly by hand, there being little potato machinery 
used except on some of the larger farms. Spraying with Bordeaux mix- 
ture is not generally practiced. 



1919] Haskell: Potato Fusarium Wilt 225 

The Disease 

The potato disease here described is one that has long been known 
under the name of "Fusarium wilt" or "Fusarium blight." Although 
the latter designation is more significant of the nature of the malady 
than is the former, still, the name "Fusarium wilt" is preferred because 
it is better known and much more widely used. The names given to 
the disease as it occurrs, on the tuber vary according to the nature of the 
injury. At harvest time affected potatoes most often show the con- 
dition variously spoken of as "stem end browning," "internal brown- 
ing," "vascular browning, " or, preferably, "Fusarium browning." Tubers 
borne on diseased vines sometimes develop a condition similar to what 
has been called "net-necrosis." The name "Fusarium necrosis" is 
suggested for this type of trouble. Such names as "Fusarium rot," "dry 
rot" and "stem end rot" have been used to designate extreme or late 
stages of the disease on this part of the host. 

It is not necessary in this paper to review the history of the investi- 
gation of this disease. The works of Smith and Swingle (14), Orton 
(9, 10), Manns (6), Carpenter (2), Link (5), and others are too well known 
to need summarizing. It is interesting to note however that the first 
description of Fusarium wilt of the potato vine itself was given in 1895 
by Prof. F. C. Stewart (15), who studied the disease on Long Island, 
N. Y., and also in the same portion of the state that was later under ob- 
servation by the writer, the lower Hudson River Valley. Stewart does 
not mention the cause of the disease with certainty, but his description 
is so complete and accurate for Fusarium wilt as it has since been diag- 
nosed by others, and as it has been noted in that region by the writer, 
that there is but little doubt that this was the disease concerned. In 
1897 Stewart (16) again called attention to this "stem-blight "in New 
York and stated that it continued to be destructive in 1896 and 1897. 

GEOGRAPHIC RANGE 

Fusarium wilt appears to be a distinctly American disease. Or- 
ton observed no typical cases during the course of a study trip through 
England, Germany, and Austria in 1911, Wollenweber (18) finds the 
Fusarium oxysporum of Smith and Swingle to be different from a European 
form, and Sherbakoff (13) speaks of the fungus as possibly occurring 
in Europe and Africa but he presents no proof that this is the case. Within 
the United States Fusarium wilt occurs widely. It has been reported 
from practically every state in the Union with the exception of parts of 
northern New England and even in this section it is probable that a care- 
ful search would reveal its presence, at least in small amounts. The 



226 Phytopathology [Vol. 9 

disease seems to be most abundant along the southern border of the 
late potato area and becomes less frequent as one proceeds northward. 
Heavy losses have been reported from many states, particularly from 
parts of New York, New Jersey, Pennsylvania, Ohio, Michigan, Indiana, 
Illinois, Missouri, South Dakota, Nebraska, Colorado, Utah, New Mex- 
ico and California. 

The disease has been observed by the writer in various parts of the 
state of New York. It has been seen most abundantly in the south- 
eastern portion, particularly in the counties of Dutchess, Orange, Put- 
nam and Westchester, and on Long Island. In some seasons, however, 
it is very common in parts of western New York, especially Onondaga, 
Ontario, Oswego and Steuben Counties. Mild cases of the disease may 
be seen almost any year in the southern and western parts of the state. 
It is only when weather conditions are especially favorable that it is 
severe. The writer has not observed Fusarium wilt in the northern 
portion of the state. If it occurs there it is not of consequence. 

ECONOMIC IMPORTANCE 

General considerations 

In the greater portion of New York Fusarium wilt is not a serious 
trouble, but in the southern Hudson River Valley, where conditions 
are favorable, it appears to be the limiting factor in potato production. 
In this region it is not uncommon to see fields with half of the plants 
dying from wilt at a time when the tubers are only half grown. The 
amount of disease varies widely on individual farms. Some fields of 
large size have been observed where it was impossible to find an entirely 
healthy plant while other fields exhibited only a few affected individuals. 
With a few exceptions, the writer did not see a field in Dutchess County, 
among the large number that he visited in 1915 and 1916, where he could 
not find the disease. 

In the spring of 1915 potatoes of the 1914 crop were examined in the 
cellars on thirty Dutchess County farms. Thirty-one per cent of these 
stored potatoes were found to be affected. The greatest amount of 
disease in any one lot of potatoes was 100 per cent and the smallest amount 
3 per cent. Tubers on all of the farms showed some of the disease and 
all but three of them had more than 10 per cent. 

Nature of the losses 

The losses resulting from the disease are of several sorts. 
1. The disease may cause an early death of the plant with the result 
that the potatoes do not attain their full size. This loss is a heavy one 



1919] 



Haskell: Potato Fusarium Wilt 



227 



when plants are affected early in the season, but if the disease is late in 
developing, the loss in this way is not so great. In an effort to get an 
idea of the amount of reduction in yield that may be brought about by 
the disease, wilted and healthy hills were dug and weighed in three dif- 
ferent fields of late potatoes of the Rural New Yorker type. It was found 
that the total yield of marketable tubers from diseased hills was less than 
one-fourth that which was obtained from healthy hills (table 1). 

2. The stem end browning in the potatoes makes them less market- 
able. Since affected tubers outwardly appear sound it often happens 
that customers unwittingly purchase diseased potatoes. This results 
in dissatisfaction on the part of the buyer. 

3. The cooking quality of the potato is sometimes impaired by the 
disease. When badly affected tubers are boiled or baked they become 
discolored and are likely to be water-soaked and soggy. 

TABLE 1 

A comparison of yields of potatoes from healthy vines and from those affected with 
Fusarium wilt, Dutchess County, September, 1916 



VARIETY 


TOTAL WEIGHT OF 
TUBERS IN TEN HILLS 


WEIGHT OF 
MARKETABLE TUBERS 


WEIGHT 


OF CULLS 




Diseased 


Healthy 


Diseased 


Healthy 


Diseased 


Healthy 


Rural New Yorker 

Sir Walter Raleigh 


pyunds 

6 
2 

31 


pounds 

12 

9 
9 


pounds 

3 
1 

2 


pounds 
11 

81 

7h 


pounds 

3 
1 

U 


pounds 
1 

3 


No. 9 


i* 






Total 


HI 


30 


6 


26f 


5^ 


3^ 







4. Waste in paring . away the affected portion sometimes represents 
a considerable loss. 

5. Diseased potatoes are unfit for seed purposes. Plants coming 
from affected seed pieces although not necessarily showing signs of wilt, 
are not so vigorous as those arising from healthy seed and the yield is 
not so large (table 3 and plate XIV). 

Estimates of the monetary losses from Fusarium wilt are very un- 
satisfactory. In 1914 F. H. Lacy, farm bureau manager of Dutchess 
County estimated the loss to be $50 per farm or $200,000 for the county. 
In 1915 the writer observed well fertilized fields of late potatoes yield- 
ing at the rate of 88 bushels per acre when at least 150 bushels should 
have been expected. A reduction in yield of 50 bushels to the acre is 
believed to be a very conservative estimate for the loss brought about 
by Fusarium wilt in Dutchess County during, that season. This would 
be equivalent to $150,000 when the market price is $1 per bushel as it 
was that year. 



228 Phytopathology [Vol. 9 

symptoms 

The symptoms of Fusarium wilt as observed in Dutchess County 
agree fairly well with those given by other writers but certain mani- 
festations have been observed in this locality that are omitted or only 
lightly treated in other descriptions. Because of this, and in order that 
there may be a clear understanding as to the disease concerned, it is 
thought well to describe the trouble here in some detail. 

On the vine 

The first visible sign of the disease on that part of the potato plant 
above ground is the appearance of a light green color of the foliage. 
As the disease develops the plant takes on a yellowish cast, while accom- 
panying the discoloration there is a rolling, wilting, and dying of the 
leaves beginning at the base and progressing upward. The upper and 
smaller leave often remain alive for some time after the lower ones are 
dead, (plates XIII, fig. A and plate XIV, fig. A). 

In the southeastern part of New York Fusarium wilt is usually not 
evident on late potatoes until about the first of August. Scattered in- 
dividual plants are usually affected first, but in many badly infested 
soils practically every plant may appear to be in an incipient stage of 
disease at about the time when the blight first begins to appear. When 
one looks at such a field from a distance a distinct mottling of light and 
dark green foliage is noticeable, the light green areas indicating regions 
in the field where the disease has made greater progress. 

On the stem and roots 

Fusarium wilt as it occurs in Dutchess County is primarily a root 
and stem rot. When diseased plants are removed from the soil care- 
fully and the underground parts washed in water the absence of many 
of the finer rootlets is very noticeable. Not only have these feeding 
roots been rotted off but all of the roots are more or less affected as in- 
dicated by a dark or brownish color contrasted with ivory white roots 
of healthy plants. Rhizomes are often attacked from the outside and 
sometimes rotted through. Lesions commonly occur on the main stem 
below ground. 

As a result of the decay of the root system affected vines fall over 
and offer very little resistance when pulled. Sometimes deep lesions 
develop on the stem near the surface of the ground and in this case aerial 
tubers may be formed in the axils of the leaves much as in the case of 
plants affected with Rhizoctonia (plate XIV, fig. C). If there is an abun- 



1919] Haskell: Potato Fusarium Wilt 229 

dant supply of soil moisture the small, topmost leaves of affected plants 
may remain alive for some time, being supplied with water by the few 
diseased or healthy roots that remain. In this case the life processes 
of the plant are maintained at a low ebb and are carried on by organs 
and tissues that are wholly or partially diseased. It is believed that 
this fact has an important bearing on the condition of the tubers that 
are produced on wilted plants. 

When the stalks are entirely dead a pink or purple coloration is often 
evident on some of the dead subterranean parts. This color is not un- 
like that produced by Fusarium oxysporum Schlecht, on certain arti- 
ficial media. 

On the tubers 

The potatoes that are borne on diseased vines are usually affected 
with an internal, vascular discoloration. The character of this affection 
varies from a slight yellowing or browning at the point of attachment 
of the rhizome to an intense darkening of the vascular elements one- 
half to two-thirds of the way through the potato. All gradations are 
found between these two extremes. This necrosis of the conductive 
tissues is very often not confined to the fibrovascular ring alone but in- 
cludes many of the smaller vessels that ramify the cortex and medullary 
tissue from both sides of the vascular ring. When potatoes badly af- 
fected in this way are cut across the stem end the flesh appears peppered 
with dark brown streaks surrounded by narrow zones of watersoaked 
tissue, a condition closely resembling what has been called "net-ne- 
crosis" (plate XV, figs. A and C). When successive slices are taken the 
brown streaks are still seen occupying the ring of fibro-vascular bundles 
and penetrating the flesh of the tuber, chiefly the outer medullary tissue. 
As the cuts are made deeper the discoloration is found to be less intense, 
finally changing to a yellow and somewhat water-soaked condition, 
and is more and more confined to the vascular ring. The extreme limits 
of discoloration are in this latter tissue, and, in severe cases, extend 
nearly to the distal or "bud" end of the tuber. Usually however there 
is not much evidence of disease in this half of the potato. 

When a tuber, affected with Fusarium necrosis, as described above, 
is pared rather deeply, so that the vascular ring is laid bare, the brown 
streaks in this tissue appear somewhat like a network radiating out from 
the stem as a center and enveloping a greater or lesser portion of the 
potato. 

Other writers on Fusarium wilt of potatoes have noted similar con- 
ditions to those just mentioned. Smith and Swingle (14: 18) reported a 
brown specking of the flesh particularly in the region of the vascular 



230 Phytopathology [Vol. 9 

ring and most noticeable at the stem end; and Manns (6: 308) shows a 
photograph illustrating the trouble. 

Affected potatoes appear sound externally. However, there are some- 
times apparent from the outside slight indications that aid in diagnosis. 
The rhizome often adheres firmly to the tuber. This may be on account 
of its being rotted off between the stalk and the potato or because of 
cessation of growth before normal abscission has taken place. Again 
a dark color may be evident on the tuber around the point of attachment 
of the underground stem. This is due to the blackened vascular bundles 
showing through the thin skin and cortex. A slight, sunken, dry rot 
is sometimes developed at this point but this is usually much more ap- 
parent on stored than on new potatoes (plate XV, fig. D). 

Under humid conditions and high temperatures in the spring, old 
tubers may become entirely rotted, in which case, the flesh becomes 
soft rotted, blackish in color, and emits a characteristic and not un- 
pleasant odor. Under moisture and temperature conditions unfavor- 
able for rot the decay is of a dryer nature and progresses very slowly if 
at all. In the cool, dry cellars of Dutchess County comparatively little 
of this storage rot develops although it is frequently observed. 

The production of spindling sprouts by affected tubers. It often happens 
in this section that when potatoes affected with vascular browning are 
taken out of storage in the spring they are found to be firmer and less 
shriveled than healthy tubers in the same lot. This is because they do 
not produce strong sprouts. Tubers badly affected with Fusarium ne- 
crosis usually send forth spindling sprouts, often so small as to resemble 
mere threads, and moderately or only slightly diseased potatoes show 
the same tendency, only to a lesser degree (plate XIV, fig. B). The depth 
to which the internal vascular browning extends into the tuber is corre- 
lated with the production of spindling sprouts by the weakened buds. 
This is a circumstance to be expected since the vascular system and the 
buds are in direct connection. The basal "eyes" are most constantly 
weakened while the strength of those toward the apical end depends on 
the extent to which the vascular tissue is affected in that portion of the 
tuber. From the results of planting trials, to be mentioned later, it 
is evident that the vigor and yield of plants from potatoes that thus pro- 
duce weak sprouts is much less than from tubers that show strong 
germination. 

ETIOLOGY 

Identity of the fungus 

The fungus associated with wilted vines and diseased tubers in New 
York appears to be identical macroscopically and microscopically with 
Fusarium oxysporum Schlecht, as described by Wollenweber (18:28) 



1919J Haskell: Potato Fusarium Wilt 231 

and by Sherbakoff (13:220). A culture of Fusarium oxysporum which 
had been determined first by Wollenweber and later by Sherbakoff was 
obtained and compared with the one consistently isolated by the writer 
from potato plants in Dutchess County, New York. In test tubes the 
two cultures appeared to be alike in every respect and when grown side 
by side in the same petri dish, where they had exactly the same con- 
ditions for growth, the mycelium of the two was identical, the colonies 
grew at an equal rate, and the same shade of coloration of the substra- 
tum resulted. The writer did not attempt to make a detailed study 
of Fusarium oxysporum except to establish its identit}'. 

Temperature relations of Fusarium oxysporum 

The relation of temperature to growth of the fungus has an impor- 
tant bearing on the occurrence of the disease. Smith and Swingle (14: 49) 
found the maximum temperature for growth to be about 37.5°C, the 
optimum 15 to 30°C, and the minimum 5°C. Link (5:26) gives 38° 
to 40°C, as the maximum, and about 30°C. for the optimum. The 
writer grew the fungus in synthetic liquid media in flasks incubated at 
various temperatures for periods of seven days each. Determinations 
of the dry weights of the fungus showed the maximum temperature for 
growth to be about 40°C. and the optimum 26 to 32°C. Cultures of 
Verticillium albo-atrum and Fusarium eumartii grown at the same time 
and under the same conditions reached their maximum limit for growth 
at 32°C, and 36°C, respectively. It will be seen that Fusarium oxy- 
sporum grows best at comparatively high temperatures and that it is able 
to withstand an unusual amount of heat. 

Pathogenicity 

Although it has long been conceded that Fusarium oxysporum 
Schlecht, is the true cause of Fusarium wilt, it is only recently that suffi- 
cient proof of this has been furnished and even now the proof is rather 
inadequate. 

Smith and Swingle (14) showed that the organism was constantly 
present in the vascular tissues of affected plants but they did not make 
any inoculations to demonstrate the pathogenicity of the fungus. 
Manns (6) made inoculations and secured infections but apparently 
he did not use pure cultures. A number of other workers have secured 
only negative or inconclusive results. Link (5) was the first to pub- 
lish results of successful infection experiments in which pure cultures 
and sterilized soil were used. He does not mention reisolation of Fu- 
sarium oxysporum but there is no doubt that it was the pathogene. It 



232 Phytopathology [Vol. 9 

should be noted however that Link did not have uniform success in 
bringing about infection. Sometimes he secured 100 per cent diseased 
plants and at other times, particularly later in the season, few or no in- 
'fections resulted. 

It is now known that Fusarium oxysporum causes a rot of the potato 
tuber under the proper conditions. This was the belief of the earlier 
workers but the proof was not forthcoming until Carpenter (2: 191) 
and Link (5:10-12) working independently, at about the same time 
and with different strains of the fungus, demonstrated that the fungus 
was capable of producing a rot of mature tubers. 

Isolations. In the course of the present investigation isolations 
were made from all parts of affected plants. They were made from the 
tubers by first disinfecting the specimens in corrosive sublimate, 1.-1000 
for ten minutes and then cutting them through a small part of the way 
with a flamed scalpel and breaking them open the remainder of the way. 
Bits of necrotic tissue were then removed from the locality desired and 
planted in petri dishes containing potato agar. Stems from which 
isolations were to be made were first washed free of soil and then disin- 
fected by soaking ten minutes in corrosive sublimate 1-1000. They 
were then split open lengthwise and the diseased portions removed with 
a sterilized scalpel. The roots and rhizomes were disinfected by wiping 
them, after they were washed, with a cloth wet with corrosive sublimate. 
Sometimes the cortex was stripped off in the process. They were then 
rinsed in sterilized water and cut into pieces for planting in agar. 

The accompanying table giving records of some of the isolations shows 
the constancy of association of parasite and host, and in what parts of 
the plant the fungus is most abundant. In making these isolations 
plantings of diseased tissue were made in plates of potato agar, slightfy 
acidified with lactic acid and containing 2 to 5 per cent glucose. 

As is indicated in the first part of table 2 the organism does not com- 
monly occur in the affected tissue inside of potato tubers affected with 
Fusarium necrosis. No growth results when disinfected potatoes that 
show the netted and streaked condition are broken open and plantings 
of diseased tissue from the interior made in media in which Fusarium 
oxysporum is known to grow well. In other words, the diseased tissue 
in the interior of tubers affected with Fusarium necrosis is sterile. The 
writer arrived at this conclusion after making repeated isolation trials 
and examining a large number of sections under the miscrocope. Smith 
and Swingle (14:18-19) found the same thing to be true. They were 
able to find neither fungi nor bacteria in the brown, specked tissue in 
the interior of affected tubers and were uncertain of the relation of this 
condition to the Fusarium disease. 



1919] Haskell: Potato Fusarium Wilt 233 

As is further indicated in table 2, the fungus is usually present in the 
extreme stem-end of affected tubers. The invasion of the tissue is or- 
dinarily shallow, however, as cultures readily reveal. Indeed pene- 
tration of the corrosive sublimate disinfecting solution into the stem 
of the potato was often sufficient to kill what little of the fungus there 
was residing there. Fusarium oxysporum is most easily obtained from 
those tubers that show a slight sunken dry-rot at the stem-end. Often 
potatoes are found where there is a decided blackening of the vascular 
bundles near the stem end, in which case the Fusarium commonly occurs 
in the blackened tissue. 

The fungus is most abundant in the roots, rhizomes, and that part 
of the stem below ground. It will be seen in table 2 that not as many 
isolations were secured from the parts of the stem at ground level as 
below ground level, and when parts of the stem still higher up are tested 
the fungus is found to be even more rare. The percentages of growth 
recorded in the table for plantings from rhizomes and roots are some- 
what deceptive. The difficulty of getting pure growth of the fungus 
was encountered and the disinfection was in some cases necessarily rather 
severe. These two facts, particularly the latter, led to a small percent- 
age of colonies. With more suitable technique it is probable that a 
much greater percentage of Fusarium growth could be secured. 

Inoculations. The constant association of Fusarium oxysporum with 
affected potato plants is in itself good evidence that the fungus is the 
cause of this vine and tuber disease as it occurs in southeastern New 
York. In order to throw more light on the question attempts were made 
to bring about infection by the use of pure cultures. 

In the season of 1915 Green Mountain potato plants growing in a 
Dutchess County field that had been in sod for seventeen years were 
inoculated with a pure culture of the fungus. The inoculum was applied 
below the ground level to wounded and to unwounded stems of various 
ages. About the second week in August some of the plants began to 
show signs of disease but so did many other plants in the 20 acre field. 
Within two weeks practically every plant in the field was affected and 
observations showed the disease to be general in the entire section. Un- 
der these conditions the infection trials were rendered worthless as all 
the plants had become naturally diseased. 

. In January, 1915, disinfected tubers of the Irish Cobbler variety were 
planted in the greenhouse in three plots of sterilized soil. In plot 1 
the soil was inoculated at once with a flask culture of Fusarium oxysporum 
growing in a liquid synthetic medium. The soil in plot 2 was inocu- 
lated later in the same way at a time when the plants were 6 inches high. 
Plot 3 was left as a check, the soil being uninoculated. About the first 






234 



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1919] 



Haskell: Potato Fusarium Wilt 



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236 Phytopathology [Vol. 9 

week in April some of the plants in all three plots began to yellow and 
die. There was no pronounced wilt or rolling of the leaves. When 
pulled up and examined some of the plants in plot 1 showed a slight 
browning of the vascular system at the base of the stem. On April 
22 plantings of diseased tissue were made in agar plates from two plants 
of plot 1 that were affected the worst and the following percentages of 
cultures of Fusarium oxysporum were obtained; plant 1, stem 100 
per cent, roots 100 per cent; plant 2, stem 80 per cent, root 0. No iso- 
lations were made from plants in other plots but it is suspected that the 
organism found its way to the check plot 3, as the condition of the plants 
in this plot was the same as those in plot 2. None of the tubers in' these 
two plots were diseased but the vines appeared slightly so. 

The temperature of the greenhouse during the experiment just men- 
tioned was kept at 18°-21°C. (65°-70°F.) in the day and 13°-15.5°C. 
(55°-60°F.) at night. It was thought that this might be too cool to be 
favorable for infection. 

With this in mind more disinfected potatoes were planted in the same 
inoculated soil and a second crop was grown in the greenhouse during 
the summer when the temperature in the house was higher. The po- 
tatoes were planted May 4 and the crop was dug and examined October 
1. Many of the new tubers showed marked stem end browning although 
none of them appeared to be affected with typical Fusarium necrosis. 
The fungus was reisolated from affected tubers and found to be the same 
as the original. The reason for success in this case and not in the other 
attempt, where the same soil was used, is attributed to the fact that 
a higher temperature was attained. It was noticed that the plants 
died first on the side of the plot toward the steam radiator pipe. It 
appeared that high soil temperatures were favorable and probably nec- 
essary for typical infection. 

Accordingly in the spring of 1917 an apparatus for regulating soil 
temperature was employed. Plants were grown in the greenhouse 
in glazed, earthenware crocks 27 cm. both in diameter and in depth. 
The crocks of sterilized soil were placed in a water-bath the temperature 
of which was under thermostatic control. The water-bath was held at 
a temperature of 36°C. (97°F.) for a period of two months. Through 
the courtesy of Dr. H. A. Edson a culture of Fusarium oxysporum, strain 
3395, was obtained from the collection at the Bureau of Plant Industry 
at Washington. This fungus was used to inoculate the soil in four of 
six crocks. A flask culture of the organism was mixed with 2 liters 
of sterilized water and was then poured on the soil immediately after 
the seed pieces were planted. The two uninoculated crocks served as 
checks. From the outset the plants growing in the inoculated soil were 



1919] Haskell: Potato Fusarium Wilt 237 

not so vigorous as the checks. They were slower in growing, and the 
leaves were smaller. Some of the lower leaves died and dropped off but 
in their place small new shoots developed. All new growth was very 
slender and spindling. 

The reason for this condition was evident when the plants were re- 
moved from the soil at the end of six weeks of growth. The young po- 
tatoes were just beginning to be formed. It was found that the whole 
root system was reduced and diseased, and on* some of the stems there 
were lesions at the base and near the point of attachment to the old seed 
piece. The xylem tissue in the diseased stems was affected for some dis- 
tance up the stem but not in that part which was above ground. Al- 
though the tops of the diseased plants did not resemble those that are 
affected with Fusarium wilt as it appears in the field, the affected root 
system and the lesions on the outside and within the stem were exactly 
like those that occur in the field. Some of the diseased roots were washed, 
dipped in alcohol and then in sterilized water, cut into small pieces, and 
planted in agar. Within a few days a number of the roots gave rise to 
a growth of Fusarium oxysporum which appeared to be exactly like the 
original strain 3395. 

This experiment was immediately repeated. Disinfected potatoes 
were planted in sterilized soil in crocks, 25 by 25 cm., that were kept in 
the water-bath at a temperature of 36°-39°C. (97°-103°F.). On March 
5, when the plants were first coming through the ground they were in- 
oculated by pouring dilute liquid cultures of Fusarium oxysporum on 
the soil. The plants grew remarkably well but with varying degrees 
of vigor. When the vines were removed June 7 and examined it was 
found that the high soil temperature had prevented the roots from go- 
ing deep into the pots. The root systems of inoculated plants were 
smaller than those of the checks, and the stalks were more slender on 
that account. An examination of the xylem of inoculated plants showed 
it to be badly discolored in most of the stems. In some instances the 
checks also showed this condition but not so badly. Isolations showed 
that the fungus had spread to the check crocks. The general superi- 
ority of the checks nevertheless showed that infection had been secured. 
Controls grown at greenhouse temperature (55°-70°F.), outside the 
bath, showed no infection and the root systems penetrated all through 
the soil in the crocks. Reisolations were made from the inside of the 
stems of four inoculated plants and 100 per cent growth of Fusarium 
resulted 



238 Phytopathology [Vol. 9 

Sources of the inoculum 

The seed. Fusarium oxysporum is undoubtedly disseminated by means 
of the seed tuber. When affected potatoes are planted the plants aris- 
ing therefrom may be diseased provided the proper conditions exist. 
Manns (6: 324-328) reports experiments that show the fungus to be 
transmitted in this way and the writer has seen instances where this 
was the case. On the other hand :' 4 often happens that affected seed 
gives rise to a comparatively healthy crop. In 1897 Prof. F. C. Stewart 
reported a planting experiment that showed this. He obtained badly 
diseased potatoes from southeastern New York and planted them on land 
that had not borne potatoes for at least ten years. Each seed-piece 
showed some of the disease. Nearly every piece grew but many of the 
plants were slow in coming up and were weak. It was late in July be- 
fore any of the plants showed the disease and then only a few of them 
became mildly affected. From this test Stewart concluded that the 
causal factor was not communicated to any appreciable extent through 
the seed but that the use of diseased seed was inadvisable because of 
low yields. 

The writer has carried on planting tests during two years and has 
had results somewhat comparable with those of Stewart. On November 
2, 1914, twelve potatoes affected with Fusarium necrosis and four healthy 
ones of the same variety, all from Dutchess County, were planted in 
a plot of disinfected soil in the greenhouse at Ithaca. The plants were 
slow in growing; partly on account of being grown in the winter, and 
were weak. Those from the diseased seed were not such vigorous growers 
as those from the healthy seed and in the end they died somewhat ear- 
lier. The plants were removed from the soil and examined April 3 at 
which time it was found that all of the new tubers were free from dis- 
ease except one from one of the affected parent tubers that showed a 
very shallow stem end browning. None of the stalks showed any sign 
of disease when split open. The plants from the four healthy seed pieces 
were unaffected also. 

In the spring and summer of 1915 planting trials were made in Dut- 
chess County that throw further light on the question of fungus trans- 
mission. Five plots were laid out in different parts of the county on 
land that had not grown potatoes for a number of years. The seed used 
in each case was carefully sorted into two lots, those tubers that showed 
distinct stem end browning being considered diseased, and those that 
showed no affection at the stem end being classed as healthy. The 
two lots of potatoes were planted side by side, cared for alike, and the 
results compared. The accompanying table shows the outcome of the 
tests. 



1919] 



Haskell: Potato Fusarium Wilt 



239 



An examination of the figures shows that the yield from the healthy 
seed was better than that from the diseased but the percentage of new 
potatoes affected was about the same in either case. The large amount 
of disease in the plants from healthy seed was unexpected. It is im- 
possible that the seed was the source of the inoculum. Infection must 
have taken place from the soil. Since both lots of potatoes were about 
equally diseased it is reasonable to conclude that not much of the organism 
could have been transmitted by way of the parent tuber. 

Further tests in which diseased Dutchess County seed was planted 
at Ithaca, New York, show that although the fungus may be communi- 
cated through the seed, yet apparently healthy plants may be secured 

table 3 

Results from planting diseased and healthy potato seed on supposedly clean land in 
various parts of Dutchess County, 1915 



LOCATION OP PLOT 



Millerton. 



Arlington. . 
Pawling. . . . 
E. Fishkill. 



Green Mountain 
Green Mountain 

No. 9 
Bovee 

Green Mountain 

Green Mountain 
Green Mountain 



Average 



AVERAGE YIELD 
PER HILL 


DISEASED 1 
RESDLTII 


Diseased 
seed 


Healthy 
seed 


Diseased 
seed 


ounces 


ounces 


per cent 


10.0 


18.5 


8 


15.0 


18.6 


4 


7.4 


13.6 


51 


7.6 


12.8 


63 


6.2 


4.6 


14 


11.3 


15.3 


80 
36 


9.6 


13.9 


37 



Healthy 
seed 

•per cent 

9 
3 

79 

81 

18 

76 

28 

42 



from affected tubers. On May 16, 1915, Dutchess County potatoes 
with stem end browning were planted in the disease garden of the De- 
partment of Plant Pathology at Ithaca. The larger tubers were split 
lengthwise and the smaller ones planted whole. Stalks came up from 
all the hills planted but many of them appeared weak, the stems being 
small in diameter and of a spindling character. After the roots had 
become well established, however, these weaker plants made better prog- 
ress and at the end of the season some of them had made a good growth 
and produced a fair yield, although not so satisfactorily as the vines 
that were vigorous from the start. The potatoes were dug September 
25 and only one hill showed Fusarium necrosis. This hill showed the 
disease in all its ten tubers, of which six were marketable. The tubers 



240 Phytopathology [Vol. 9 

from this hill were kept and planted June 9 of the following season. 
Some of the resulting vines were weak while others gave a fair growth. 
Toward the middle of August they looked rather poorly. When dug 
two hills out of seven had no tubers while potatoes from two of the 
five remaining hills showed a little stem end browning. 

In June of the same year (1916) at Ithaca nineteen hills were planted 
with affected seed from Dutchess County. When dug in the fall the 
potatoes in seven out of sixteen hills were affected, those in two hills 
being distinctly diseased, and those in the other five only slightly so. 

These planting experiments bear out the author's conclusion regard- 
ing the nature of the disease. They show that the causal factor may 
be communicated to some extent at least through the seed tubers. On 
the other hand diseased seed often gives rise to plants that produce a 
healthy crop. This may be either because those tubers do not harbor 
the pathogene or because it is present but conditions are unfavorable 
for sufficient development. Both of these reasons are quite possible. 
The trials further emphasize the fact that affected potatoes are very 
likely to produce weak and spindling plants with a resulting lowering 
of yield, and that infection from the soil is a more important means of 
communication. 

The soil. The soil is the principal source of the inoculum and it is 
when infection takes place from this source that the disease is at its worst. 
The results of planting healthy and diseased potatoes on land that had 
not produced potatoes for several years (table 3) show the soil to be more 
important than the seed as a source of the organism. After the fun- 
gus is once established in the land it becomes very persistent, and it is 
the opinion of the writer that if conditions are favorable it may exist 
there even in the absence of the potato crop for an almost indefinite 
length of time. In Dutchess County a field was observed which had 
not been plowed for seventeen years and yet when this old pasture land 
was planted to fusarium-free, Green Mountain potatoes from Maine in 
1915 the resulting crop was uniformly diseased. In the summer of 
1915 many potato fields in Dutchess County were visited and it was 
common to find new potato land which had been planted with unaffected 
seed producing a crop that showed the typical symptoms of Fusarium 
wilt. On the other hand it was equally common to find fields that were 
more or less free from the disease. This is accounted for not so much 
by the fact that the organism was not present but because environmental 
conditions were unfavorable for infection and development. 

In an attempt to demonstrate that the disease is transmitted by means 
of infested soil the writer conducted a greenhouse experiment along the 
same lines as did Manns (6 : 316-317) and with somewhat similar results. 



1919] 



Haskell: Potato Fusarium Wilt 



241 



In the spring of 1916 Irish Cobbler potatoes were selected that showed 
no internal browning of any kind. They were disinfected in corrosive 
sublimate 1-1000 for one and one-half hours and planted in the green- 
house in two plots of soil which came from a field in Dutchess County 
that produced a badly diseased crop in 1915. The soil in one of the 
plots, the check, had been previously sterilized by subjecting it to 15 
pounds pressure of steam for one hour. There were twelve hills in each 
plot. At about the time when the tubers were setting, some of the plants 
in the unsterilized soil began to appear rather sickly but did not show 
the typical symptoms of Fusarium wilt as seen in the field. When the 
plants were removed on April 22 it was found that some of the root sys- 



TABLE 4 



Results of isolations from various parts of potato plants grown in sterilized and 
unsterilized Dutchess County soil in the greenhouse 1916 



SOIL 


PART OP PLANT FROM 

WHICH 
ISOLATION WAS MADE 


NUMBER OF 
PLANTINGS 


PERCENTAGE OF 
FUSARIUM 




f 

Tubers, inner part { 

I 

Roots < 

Rhizomes 

[ 
Roots I 


5 
5 
5 

12 
12 

6 

12 
12 
10 
10 






100 
100 

50 








terns in both plots were unhealthy. Three potatoes were found that 
had the typical stem end necrosis as seen in Dutchess County. No 
such tubers were found in the check plot. Isolations were made from 
some of the diseased plants in both plots with results as shown in table 4. 
Although the isolation trials from roots grown in sterilized soil gave 
no Fusarium oxysporum they revealed the presence of a species of Ver- 
micularia in amounts ranging from 15 to 75 per cent. The roots grown 
in the unsterilized soil showed the constant association of Fusarium 
oxysporum. The temperature of the greenhouse had been allowed to 
run at 15.5°-18°C. (60-65°F.) during the daytime and at 10°-13°C. (50- 
55°F.) at night, which, it should be stated, is far too low for optimum 
development of the fungus and disease. 



242 Phytopathology [Vol. 9 

Land that has produced a diseased crop one year is practically cer- 
tain to do so the next if potatoes are planted. In 1915 the writer con- 
ducted some variety and fertilizer experiments on land that had pro- 
duced a diseased crop the previous year, using seed free from Fusarium. 
In both instances the disease was abundant in 1916, there being any- 
where from 31 to 88 per cent affected tubers in the various plots. There 
were numerous instances of this kind observed in 1915 and 1916 where 
healthy seed was put on land that produced a diseased crop the year 
before and in no instance did the blight fail to manifest itself. 

Manure and refuse. Smith and Swingle (14 : 53) suggested the ad- 
visability of avoiding soil contamination by means of infested manure. 
Orton (9 : 7) pointed out that dead tops and small and diseased tubers, 
left upon the ground furnished a breeding place for the wilt fungus. 
Manns (6 : 322) made the statement that partially rotted tubers and 
refuse from storage ought not to be thrown on the manure pile as it was 
a sure way of introducing the organism into the field. 

Manure and refuse are doubtless one of the sources of the inoculum 
but it seems improbable that this source is an important one. These 
substances act as carriers of the fungus but it is believed that efficient 
dissemination would be accomplished even in their absence. 

Agents of dissemination 

Dissemination of the fungus with the seed manure and refuse, and 
also during the process of cultivation is attributable to man. Wind 
and water, however, are believed to be more important agents of dis- 
semination. The organism is undoubtedly blown long distances along 
with dust. The widespread and general occurrence of the fungus in 
regions where the disease occurs would lead one to suspect that this 
was so. The washing of the infested soil by surface water from one 
field to the next and also the carrying and depositing of the organism 
by streams are probably important modes of dissemination in some 
places. 

Infection 

When the pathogene is introduced with the seed infection may take 
place at the base of the sprout or stalk as the vascular systems of the 
parent tuber and stem are in direct connection. It is possible also that 
the fungus may assist in rotting the seed piece and from it grow out in- 
to the soil where it is in a position to affect the roots. 

When the soil is the source of the inoculum, as it most often is, the 
roots, especially the smaller ones, are the principal channels through 



1919] Haskell. Potato Fusarium Wilt 243 

which the fungus enters its host. It is apparent too that the organism 
may attack the seed from the soil and from there gain entrance to the 
main stem. Rhizomes and parts of the stem under ground also may 
be attacked directly from the soil. It is not uncommon to find young 
potatoes completely cut off from the parent plant because of attacks 
on the rhizomes. Growth cracks in the stem undoubtedly favor the 
penetration of the organism and numerous stem lesions, that appear 
to have been made by the entrance of the fungus through the unbroken 
epidermis, have been seen. The new tubers usually are inoculated by 
way of the rhizomes on which they are borne. 

Within the roots the mycelium develops rapidly or slowly depend- 
ing on temperature, moisture and other conditions. The hyphae ap- 
parently penetrate all tissues of the root, killing it and rendering it 
useless for absorption. The root becomes brownish in color in marked 
contrast to the ivory whiteness of those that remain healthy. The 
effect of the injury is manifested by a slowing of growth, a change in 
color of the leaves and later by a rolling or wilting of the foliage. The 
mycelium progresses lengthwise through the root, particularly within 
the xylem, which offers the path of least resistance. In this, and prob- 
ably in other tissues of the root, the fungus makes its way to the main 
stem. The writer finds that when a diseased stem is cut the tissue that 
appears most affected is the phloem. It is quite dark-brown in color, 
due to a breaking down of the cells, particularly the sieve tubes. Be- 
cause of this necrosis the underground parts of affected stems appear 
somewhat darkened on account of the brown, dead tissue showing through 
the cortex and unaffected epidermis. 

The xylem appears to become affected at about the same time as the 
phloem. \l\ parts may be affected, the tracheae with companion cells 
being the most so, and the wood cells the least. It is within the tra- 
cheae that the fungus makes its greatest progress and it is in these cells 
that the mycelium is most easily discerned with the microscope. The 
medullary rays are quick to become discolored and, as they take on a 
darker brown coloration than the xylem, they often show up quite con- 
spicuously. In later stages of the disease the cortex, epidermis, and 
pith become successively affected. The mycelium penetrates cell walls 
quite readily as it can be seen extending from one cell to the next, usu- 
ally through pits and thin places in the walls. The fungus does not 
penetrate far into the portions of the stem above ground but rather 
confines itself to subterranean parts. The interior of the aerial parts 
of the stem usually appears fairly normal to the naked eye and micro- 
scopic examination, as well as isolations such as are described in table 2, 
usually show the fungus to be very scarce or entirely absent at points 
6 inches or more above the ground level. 



244 Phytopathology [Vol. 9 

As the disease progresses the roots become completely decayed. New 
ones may be pushed out near the surface of the ground and above the 
badly diseased part. Meanwhile the majority of the leaves die, the trans- 
piring area being reduced to equalize the absorbing surface. Such plants 
fall over for lack of support, linger along for some time and finally die. 

Affected tubers are always borne on vines which show evidence of 
having Fusarium wilt. The degree of infection of the tuber varies accord- 
ing to the severity of the disease as it appears on the top. It commonly 
occurs that one stalk in a hill is diseased and another stalk is compara- 
tively healthy, and when the whole plant is carefully removed from the 
soil it is found that the tubers clinging to the affected stem are diseased 
while those produced on the healthy part are entirely sound. Tubers of 
all sizes are attacked although the larger ones seem to be more liable to 
show deep infection. 

As far as has been observed Fusarium necrosis does not increase in 
storage. Under warm and moist conditions affected potatoes will gradu- 
ally become rotted, as will also many tubers not so affected, but the 
necrotic condition itself does not tend to become greater. 

Pathological physiology 

Theories as to the cause of necrosis of the tuber accompanying wilt of the vine. 
It has been mentioned that tubers affected with Fusarium wilt as it occurs 
in southeastern New York commonly exhibit a necrosis of the vascular 
system, and that usually the organism is not present in the diseased 
tissue except at the extreme stem end and in places that show an in- 
intense browning. Various theories may be advanced to explain this. 

It is possible that extremely unfavorable environmental conditions 
may be the cause of necrosis of the vascular system in the absence of 
any organism. For example it is now known that a condition of frost 
necrosis may be brought about by chilling, or frosting. It has been 
suggested also that overheating may possibly act in the same way as 
it is found that the vascular system of the tuber is the most sensitive 
tissue to feel the effects of adverse conditions. It has been suggested 
further that an insufficient water supply may result in a browning of the 
vessels. It seems improbable that any of these factors should be re- 
sponsible for the stem end vascular necrosis that accompanies Fusarium 
wilt. Under natural conditions it certainly is not brought on by chill- 
ing and if heat was the causal factor one would not expect to find the 
disease localized in one end of the tuber nor would there be such a close 
relation between diseased tubers and wilted vines. It does not appear 
to be a water relation as it has been observed to occur under very wet 
as well as in very dry conditions. 



1919] Haskell: Potato Fusarium Wilt . 245 

The theory that one or more toxines are responsible is much more 
plausible. Investigations conducted by the Federal Department of 
Agriculture 2 and also by the writer have shown that stem end browning 
can be artificially produced by feeding toxic materials in solutions at 
strengths too weak to kill the plant at once but of sufficient concentra- 
tion to act upon the vascular system of the stem and tuber. 

For injecting the solutions into plants the writer employed a method 
similar to that used by Miss Rumbold (12:225-228) in her work with 
trees. For containers, gas chimneys with two-holed rubber stoppers 
in the lower ends were used. Glass tubes were inserted in the two holes 
in each stopper and rubber tubes about 45 cm. long were attached. In 
the ends of these were placed pieces of glass tubing the ends of which 
were bent and drawn out to capillary fineness. When in use the chim- 
ney was elevated above the plant and secured to a stake. It was then 
filled with the solution and the needle-like ends of the capillary tubes 
inserted in the stem or rhizome of the plant. Stop-cocks on the rubber 
tubes aided in manipulation. 

To determine the possibilities of the method a weak solution of eosin 
was first used. In one case it was introduced through a side shoot. 
The dye penetrated down the stem in the water vessels of the xylem 
and into the old seed tuber. It also traveled up the main stem for some 
distance but it did not go out into the newly formed tubers. When 
the capillary tube was inserted in the rhizome, however, the solution 
penetrated through the vascular ring almost to the apex of the young 
tuber. 

On March 15, 1916 an experiment was started as follows: 5 per cent 
oxalic acid was introduced into four plants; a saturated solution of 
salicylic acid into two plants; 1 per cent galactose into two plants; and 
Czapek's solution for fungi, in which Fusarium oxysvorum had been 
growing for about three weeks, containing extra-cellular enzymes of the 
organism, into two plants. The capillary tubes were inserted for the 
most part in the lower portion of the stems although in a few cases the 
solutions were introduced into the rhizomes. 

After six days all the plants were removed and examined. All the 
stems into which oxalic acid had been injected were dead, whitened, and 
shrunken for some distance above the point of insertion of the needle. 
Above the killed area the fibro-vascular bundles were blackened up into 
the leaflets and some of the leaves showed a spotting of the parenchyma 
between the smaller veins. The vascular ring of one tuber, borne on 
a plant into the stems of which oxalic acid had been introduced, was 

2 Unpublished information gained from conversation with Drs. H. A. Edson, 
W. A. Orton, and others. 



246 . Phytopathology [Vol. 9 

browned inward for some distance and resembled very much the internal 
browning accompamdng Fusarium wilt. Some of the tubers borne on 
rhizomes that were injected with oxalic acid showed a similar condition 
(plate XV, fig. B). 

Stems into which salicjdic acid was introduced showed dead and 
shrunken areas in the immediate vicinity of the needle, with one of 
the primary bundles blackened for a distance of about 8 cm. The 
tubers did not seem to be much affected with this substance. Galac- 
tose at the concentration used was without appreciable effect. The 
solution in which the fungus had grown gave good results. When in- 
oculated into rhizomes not far from growing tubers the vascular system 
of these organs and of the tubers became affected and the latter showed 
a brown ring as seen in Fusarium wilt, but the condition resembling 
net-necrosis was not reproduced. The inoculum was prepared by grow- 
ing Fusarium oxysporum in Czapek's solution for about three weeks at 
the end of which time the fungus was removed and the liquid medium 
containing the enzymes that had been excreted by the mycelium during 
its growth was filtered off. It had a noticeably bitter taste at this time^ 
No attempt was made to keep the extract sterile after it was filtered nor 
while it was being injected into the plant. There was no growth of 
any kind on the surface during the length of the experiment. 

From these results it is evident that certain toxic substances when 
introduced into the vascular system of a growing potato tuber may 
cause a browning of the vessels. It seems probable that stem end 
necrosis with its absence of any organism can be explained on this basis. 

The toxic material involved may be excretions of the fungus, as has 
been shown by the foregoing experiment, or it may consist of decom- 
position products from dead host cells. In Overton's (11) work on the 
relation of living cells to the ascent of sap it will be recalled that he had 
occasion to kill portions of Cyperus stems with steam. He found that 
leaves on stems so killed did not wither as quickly as did cut stems in 
water, but when they did die they showed all the symptoms of being 
poisoned rather than simply deprived of water. When steamed stems 
were split lengthwise numerous dark streaks or lines could be seen with 
the naked eye in the vascular tissue above the killed portion, reaching 
almost to the leaves in some cases. The streaks followed the fibro-vas- 
cular bundles and ranged in color from black to brown and yellow. The 
phloem was the part that was most deeply colored, apparently due to 
a disorganization of the sieve-tubes. A mucilage or gum-like substance 
which in some cases plugged the xylem vessels was observed to be present 
in the tissue above the killed portion. 



1919] Haskell: Potato Fusarium Wilt 247 

In the spring of 1916 the writer killed potato stems with steam. The 
lower portions of stems of plants growing in the greenhouse were killed 
by steaming them in a glass chamber such as was used by Overton and 
also by simply playing a jet of steam on the part to be killed. The leaves 
on plants so treated stayed quite turgid for a number of days. One of 
the plants continued to appear normal for four days after treatment, 
and then the leaves finally showed the effects by slowly wilting, turn- 
ing yellow and finally by dying. Some of the leaves showed a mottling 
of dark and light green not unlike mosaic and one plant produced aerial 
tubers in the axils of the leaves all the way up the stems. When the 
stems were split open most of the plants showed a blackening of some 
of the bundles above the lesions and in one case a browning of the bundles 
of a tuber was observed. 

These observations show that the decomposition products of potato 
cells which have been killed by steam are able to discolor the water- 
carrying tissue and are probably toxic to it. It is believed that the toxin 
theory is the most plausible explanation for vascular discoloration in 
potato tubers borne on affected plants. The root, stem and rhizome 
tissues are diseased and many cells are dead. The plant, however, con- 
tinues to function at a low ebb. The yellowed and small leaves continue 
to synthesize carbohydrates which are transported to the tubers through 
vessels that are thoroughly diseased. Toxic products from decomposing 
cells and from fungus mycelium become mixed with the sap and are 
transferred with it to the tuber where they affect the net-like system 
of tracheal tubes. The result is a stem end net-necrosis with no organism 
present. 

Further theories as to the cause of wilting. During the summer of 1915 
the writer carried on a small experiment that further substantiates the 
conclusions of Overton (11) and Dixon (3 : 68) that products of plant 
cells are toxic to the plants themselves and that wilting may be due to 
the introduction of poisonous or plasmolyzing substances into the tran- 
spiration sap. Cut stems of potato plants were placed in bottles con- 
taining extract of ground pulp from healthy and from diseased potato 
tubers. The extract was prepared by grinding the potatoes, washing 
with tap water, and filtering out the diluted juice. The bottles were 
arranged in series as follows : 

Series 1. Three bottles, 150 cc. tap water in each. 

Series 2. Three bottles, 150 cc. tap water containing extract of healthy 
potatoes. 

Series 3. Three bottles, 150 cc. tap water containing extract of potatoes 
affected with Fusarium necrosis. 



248 Phytopathology [Vol. 9 

Fresh shoots were placed in the solutions and at the end of nineteen 
hours the following notes were taken: 

Series 1. All plants erect, turgid, and as fresh as if growing in field. 

Series 2. Decided wilt. Stems very flaccid, tops bending over and 
touching table. 

Series 3. Decided wilt, about the same as series 2. 

This experiment coupled with the result of other investigations (11,3) 
leads one to suspect that the extract from both diseased and healthy 
tubers had a poisonous effect on the green shoots. 

Certain wilt diseases of plants, Fusarium wilt of potato included, have 
been attributed to direct stoppage of the vessels with hyphae of the re- 
spective causal fungi, thus shutting off the supply of water to the leaves. 
This may be a factor in some cases but it has very little effect as far as 
Fusarium wilt of potato is concerned. The writer has examined the 
stems of many plants microscopically and found no instance of a stoppage 
of the trachea sufficient to shut off the passage of sap. The destruction 
of the roots is enough in itself to explain the rolling, wilting and death 
of the leaves and that is believed to be the primary reason for the early 
death of affected plants. 

ECOLOGY 

Influence of climatic factors 

Temperature. It is well known that the potato plant needs a cool 
growing season for its best development. High summer temperatures 
do not obtain in its native habitat in the mountainous regions of Peru 
and Chili, and the plant is found growing most vigorously and produc- 
ing the largest yields in the northernmost and coolest parts of the United 
States. It is true that potatoes are successfully grown in certain parts of 
the southern states but in these places the greater part of the crop is grown 
during the early and cool part of the season and early varieties are used 
especially. In this way the crop is matured before the hottest weather 
of the summer. The yields obtained are not large and it is the high 
price that is annually secured for an extra early product that makes the 
crop profitable. 

In the northern part of New York yields of 300 and 400 bushels 
per acre are not uncommon while in the lower Hudson Valley 200 
bushels are. exceptional. This is due chiefly to the higher temperature 
in the latter region. An examination of the temperature records of the 
United States Weather Bureau shows that the hottest part of the state 
during the summer is from Poughkeepsie south to New York City. 



1919] Haskell: Potato Fusarium Wilt 249 

It has already been pointed out that Fusarium oxysporum was able 
to resist high temperatures and that it makes its optimum growth at 
temperatures of 26°-32°C. (79°-89°F.) and its maximum is in the neigh- 
borhood of 40°C. (104°F). It is evident then that hot weather is un- 
favorable for the host but is favorable for the parasite. Furthermore 
it appears that it is during hot weather that the wilt develops and it is 
noticeable that the disease occurs in places where high summer tem- 
peratures prevail. In the United States it is most common all along 
the southern border of the late potato regions. In New York it is especi- 
ally in the southeastern part, and somewhat, although not so common, 
in the western, central and southern sections. In Dutchess County 
it is most severe in the southwestern part where the summer temperature 
is the highest. The village of Wappingers Falls, Dutchess County is 
about in the center of the region where the disease is worst. At this 
place is located one of the United States Weather Bureau cooperative 
stations. It is interesting to compare the summer temperatures here 
with the average of the Hudson River Valley and of the state (table 5). 

It will be seen that the temperatures at Wappingers Falls are about 
the highest in the Hudson Valley Division which includes the counties of 
Albany, Greene, Saratoga, Putnam, Columbia, Warren, Rensselaer, 
Fulton, Dutchess, and Orange. It is further evident from the table 
that the highest monthly mean temperatures in the state are registered 
in the Southern Hudson Valley at stations from Troy south to New 
York City. In 1914 the highest temperatures in the state for the months 
of September and October were recorded at Wappingers Falls. Manns 
(6 : 319) gives the mean temperatures at Wooster, Ohio, for June, July, 
August and September of the years 1908, 1909 and 1910 when Fusarium wilt 
was serious. The figures are very much like those for the mean tempera- 
tures during the same months at Wappingers Falls, Dutchess County 
in the years 1914 and 1915, in fact the average means for the seasons 
are nearly all alike. 

Within Dutchess County a distinct correlation between altitude and 
amount of disease was noticed. Fusarium wilt might be severe on the 
lowlands near sea-level but a few miles distant up on the hills and ridges 
at an altitude of about 1000 feet the disease was rare. From conver- 
sations with farmers it was learned that larger yields were obtained on 
the highlands and that in those places Fusarium wilt had never been 
a serious factor. This variation in amount of disease is attributable 
principally to difference in temperature. In an effort to determine how 
much variation in temperature could be expected at higher and lower 
levels in the county, temperature records were taken on Chestnut Riclge 
at an altitude of 1140 feet and at Rochdale, a place 14 miles further west, 
which is 200 feet above sea-level. The results are given in table 6. 



250 



Phytopathology 



[Vol. 9 



TABLE 5 



Summer temperatures at Wappingers Falls, New York, compared with the average for 
the Hudson River Valley and for the state, 1914 and 1915 



MONTH 


WAPPINGERS FALLS 


HUDSON VALLEY DIVISION 




Mean 


Highest 


Lowest 


Mean 


Highest 


Lowest 


1914 


68.0 
70.9 
72.9 
64.2 


96 
91 
97 
99 


42 

48 
50 

28 


65.5 
69.1 
69.5 
61.7 


97 
93 
97 
99 


38 




42 




39 


September 


20 








69.0 






66.4 










1915 

June . 


68.0 
72.0 
69.4 
67.6 


92 
94 
90 
94 


40 
50 
46 
35 


65.5 
70.3 
67.2 
66.2 


92 
94 
91 
94 


34 


July 


45 


August 


40 




29 






Average 


£9.2 






67.3 







New York State 





MEAN 


HIGHEST TEMPERATURE IN STATE 


LOWEST 


HIGHEST MONTHLY MEAN 




Temper- 
ature 


Place 


Temper- 
ature 


Place 


1914 
June 


63.6 
68.2 

67.7 
59.6 


99 

98 

103 

99 


Mount Hope 
Troy 

Fayetteville 
Wappingers Falls 


29 
31 
30 
18 


69.8 
72.8 
73.7 
67.3 


West Point 


July 

August 


Troy 

New York 


September 


Citchogue 


Average 


64.8 












1915 

June 

Julv 

August 

September 


63.1 
68.0 
65.5 
63.9 


94 
95 
94 
95 


Brockport 
West Berne 
Bedford Hills 
West Berne 


30 
23 
29 
24 


68.3 
73.2 
71.6 
69.0 


Mount Hope 
West Point 
Bedford Hills 
West Point 


Average 


65.1 













It will be seen that as a rule it was cooler at the higher altitude. The 
temperature there was more uniform and at no time did the thermometer 
go above 95°F. while at the 200 foot level the temperature rose to 100°F. 
at four different times. 



1919] 



Haskell: Potato Fusarium Wilt 



251 



TABLE 6 



Record of temperatures at Rochdale, Dutchess County, altitude 200 feet, compared with 
those at Chestnut Ridge, H miles east, altitude 1200 feet. July 25, to August 27, 1916 



July 25 

July 26 

July 27 

July 28 : 

July 29 

July 30 

July 31 

August 1 

August 2 

August 3 

August 4 

August 5 

August 6 

August 7 

August 8 

August 9 

August 10 

August 11 

August 12 

August 13 

August 14 

August 15 

August 16 

August 17 

August 18 

August 19 

August 20 

August 21 

August 22 

August 23 

August 24 

August 25 

August 26 

August 27 

Average for 34 days 



MAXIMUM 


MINI 


Rochdale 


Chestnut 
Ridge 


Rochdale 


deg. F. 


deg. F. 


deg.F. 


82 


78 


65 


75 


71 


65 


90 




70 


85 


74 


62 


80 


79 


46 


63 


82 


57 


87 


89 


64 


84 


77 


57 


87 


83 


48 


83 


86 


49 


90 


83 


59 


90 


85 


66 


100 


88 


70 


97 


89 


70 


100 


91 


75 


89 


77 


67 


65 


63 


57 


73 


71 


54 


90 


87 


60 


73 


73 


53 


81 


75 


39 


85 


86 


44 


89 


87 


51 


92 


82 


57 


93 


89 


54 


95 


86 


56 


97 


86 


55 


100 


89 


54 


. 101 


87 


62 


100 


94 


63 


77 


70 


60 


86 


83 


44 


88 


82 


54 


87 


81 


59 


85.7 


79.2 


56.9 



Chestnut 
Ridge 



l.F. 



65 
64 

62 
53 
68 
69 
59 
53 
53 
60 
65 
69 
68 
67 
63 
53 
53 
60 
49 
46 
52 
52 
63 
60 
60 
61 
60 
68 
62 
58 
53 
59 
59 



59.6 



The writer has noticed a tendency for Fusarium wilt to occur more 
abundantly on southern than on northern exposed fields. Bouyoucos 
(1: 125) has shown that a southern exposure of a field considerably in- 
fluences soil temperature. According to him a southern exposure had 



252 Phytopathology [Vol. 9 

about 2°F. higher average temperature than a northern during the spring 
and summer months of 1915. Bouyoucos (1 : 132) has also demons- 
strated that shade has a very large controlling influence upon soil tem- 
perature. The writer has made observations showing that Fusarium 
wilt is reduced by shade. In 1916, a potato field was observed on the 
edge of which stood a tall elm tree that cast a shadow during the middle 
of the day on some of the vines in the vicinity. The plants thus shaded 
were green and only slightly affected with Fusarium wilt while other 
plants in the same field were entirely dead from this disease and tip-burn. 
It is believed that the soil moisture relation did not enter in as an in- 
fluencing factor in this case. In 1916 the writer kept continuous tem- 
perature records by means of a soil and air thermograph. It was found 1 
that shade afforded the soil by potato vines was considerable. The 
maximum temperature of unshaded soil, at a depth of 4 inches, was 9°F. 
higher than soil that was shaded by vines. It was found that covering 
the soil with a straw mulch greatly tends to keep down and to equalize 
soil temperature. 

These facts coupled with the results of infection experiments in the 
greenhouse, where the temperature was controlled, lead to the belief 
that temperature is probably the most important factor limiting the 
development of Fusarium wilt in southeastern New York. It is thought 
that the organism is widespread in many soils and that in the majority 
of cases it only awaits the presence of the potato crop and the proper 
temperature conditions to develop. 

Rainfall. It is believed that the amount of rainfall has very little to 
do with the prevalence of the disease. In the year 1915 when there 
was an abundant supply of moisture to the plants Fusarium wilt occurred 
to about the same extent that it did in the summers of 1914 and 1916 
when there was dry weather. It seems, however, that under conditions 
of drought diseased plants will succumb quicker than when supplied 
with sufficient water. 

Influence of soil factors 

Fusarium wilt in New York is not confined to any particular type 
of soil although it appears to be more common on the lighter sandy soils 
than on heavier clayey ones. Orton (10:8) pointed out that Fusarium 
wilts of cotton, watermelon, and cowpea occurred principally on sandy 
and sandy loam soils but that such was the case with potato wilt was 
not certain, although the evidence indicated that the plants on light 
soils were more liable to infection. In New York potatoes on clayey 
soils are affected but usually not so badly as on the other more sandy 
types. It is believed that the relation of soil type to disease is princi- 



1919] 



Haskell : Potato . Fusarium Wilt 



253 



pgjly because of differences in temperature. Clay soils have a greater 
water-holding capacity and are cooler on that account. Sandy soils 
are not able to hold so much water and are therefore hotter. Dark 
colored soils like muck would naturally become warmer than light colored 
ones on account of their heat absorbing capacity but this may be offset 
by the large water content. 

It was believed in the early part of this work that certain chemical 
properties of the soil might be influential in bringing on stem end net- 
necrosis of the tuber. Various types of internal browning occurring 
both in the United States and Europe have been ascribed to malnutri- 
tion and unfavorable soil conditions. Certain of these troubles have 
been attributed to lack of potash, lime, or phosphate while some workers 
have thought an excess of iron was responsible. In order to test the 
effect of various soil treatments on the disease a strip of land, 10 by 

TABLE 7 

Results of planting healthy seed on infested land in Dutchess County, the soil being 
treated with various fertilizers 



TREATMENT 



Average of 3 nitrate soda plots 

Average of 3 phosphoric acid plots. . . 
Average of 3 muriate of potash plots. 
Average of 3 complete fertilizer plots 

Average of 3 lime plots 

Average of 15 check plots 



AVERAGE 

WEIGHT PER 

HILL 



6.1 
14.7 
6.0 
9.07 
9.2 
8.79 



DISEASED 
TDBERS 



per cent 

43 

77 
63 
71 

72 
67 



100 yards, was selected in a field where there has been considerable 
of this trouble the year before. The strip was divided into plots 
running crosswise, and disinfected; fusarium-free, Green Mountain 
potatoes were planted. The fertilizers were placed in the furrow and 
mixed with the soil before the seed was dropped. Check plots were 
placed between each test plot and the experiment was run in triplicate. 
The substances used and a summary of the results obtained are given 
in table 7. 

The results obtained are in accord with those of Smith and Swingle 
(14 : 27) who carried on extensive fertilizer experiments, using many dif- 
ferent substances and in varying amounts. As will be seen in table 7 
none of the various treatments had any appreciable effect on the amount 
of disease. The percentages were obtained by cutting through the stem 
end of every potato in the center row of each plot. A large proportion 
of tubers in all plots showed typical Fusarium necrosis. 



254 Phytopathology [Vol. 9 

CONTROL 

Crop rotation 

It has been advised by various workers that rotation of crops will 
aid in keeping down the disease. Manns (6 : 333) recommended the 
allowance of at least five or six years between successive crops, Orton 
(10 : 14-15) advised five to eight years, and Smith and Swingle (14 : 53) 
pointed out the advisability of crop rotation but mentioned no definite 
period. After seeing so many outbreaks of Fusarium wilt on new po- 
tato land where clean seed was planted, the writer is inclined to doubt 
the value of rotation as a method of control. Attention has already 
been called to a field which had not been planted to potatoes for seven- 
teen years and practically every plant in which became affected. In 
New York state the fungus appears to be generally distributed over 
large areas and seems to be very persistent when once established. Ap- 
parently it only awaits the potato crop and favorable conditions to 
become destructive. 

It is believed, as a matter of general principle, and in order to hinder 
the development of the fungus as much as possible, that a wide rotation 
of the potato crop is advisable in sections where Fusarium wilt is liable 
to occur. Certainly in such locations potatoes should not be planted 
two years in succession on the same piece of land. 

Elimination of diseased tubers or parts of tubers 

It is advised that the use of diseased potatoes be avoided in the ma- 
jority of cases. Not only is it possible that the fungus may be trans- 
mitted from one crop to the next in this way and the soil become more 
thoroughly infested by so doing, but, as has been pointed out, the sprouts 
of potato tubers affected with Fus'arium necrosis are weakened and the 
resulting plants are not so strong, nor is the yield so great, as when healthy 
seed is used (table 3). 

It is advised that wherever possible northern grown, fusarium-free 
seed be secured for planting, but, in case native seed is used, the follow- 
ing procedure is recommended. Representative samples should be 
taken from the stock under consideration for planting and an examina- 
tion made by clipping slices from the stem end of a number of tubers. 
If a considerable percentage (5 per cent or over) of the tubers are found 
having marked Fusarium necrosis it is believed that the entire stock 
should be rejected for seed purposes. If only a small percentage is found 
the seed may be good for planting, providing the badly diseased tubers 
are removed. This may be largely accomplished in two ways, (1) by 



1919] Haskell: Potato Fusarium Wilt 255 

germinating or "greening" the potatoes for a few weeks before they are 
planted and then using only those tubers that show strong germinative 
power for seed, or, (2) in case the seed is to be cut as it usually is in 
Dutchess County, the stem end of each tuber may be clipped during the 
process of cutting and diseased tubers discarded. It is believed that the 
"greening" process mentioned above, in which the potatoes are spread 
out in a dry light place two to three weeks in advance of planting, is 
worth while anyway as it insures the use of strong seed and gives a 
quicker come-up and earlier yield, a factor which in itself, as will be 
shown later, is helpful in avoiding the disease. In case slightly dis- 
eased cut seed is being used for planting it is believed desirable to re- 
move and reject the stem end of all tubers during the cutting operation. 
It does not take much longer, it shows to what extent the tuber is af- 
fected, and it frees the seed piece from the diseased part where the or- 
ganism may be harbored. If the buds on potatoes that show ring in- 
fection appear strong there is no reason why the healthy part should 
not be planted provided the entire diseased portion is removed. It 
might be safer not to use such seed as a number of other diseases of a 
more communicable character produce a somewhat similar ring discolo- 
ration. On the other hand if one is familiar with the disease and the 
seed is otherwise good it would doubtless be economy to plant the healthy 
and vigorous appearing portion as suggested. 

Along with inspection should go seed treatment to kill various patho- 
gens including Fusarium on the exterior. Manns (6 : 332) recommends 
disinfection after the stem ends have been removed but on account of 
possible injury through the cut surface it would seem much more pref- 
erable that the treatment precede cutting. Dusting the cut seed with 
sulfur flour or flowers of sulfur is believed to be advisable both as a general 
cultural practice and because of possible disinfecting properties against 
Fusarium. 

Disease resistant varieties 

In the case of a number of other plant diseases of this nature such 
as cotton wilt, cowpea wilt, and cabbage yellows the development and 
growing of resistant plants has offered the most satisfactory, and in 
some cases the only method of effective control. It is probable that 
in time varieties of potatoes resistant to Fusarium wilt will be secured 
by selection or hybridization but thus far none have been obtained. 

The writer has made trials with a few varieties on infested soil in 
Dutchess County. On May 25, 1915, five different varieties of potatoes 
were planted on land that had produced a badly diseased crop the year 
before. It was made certain that the seed was free from any vascular 



256 



Phytopathology 



[Vol. 9 



browning by clipping off the basal end of each seed tuber before planting. 
When harvested, September 14, the yield and amount of Fusarium stem 
end browning was ascertained and is given in table 8. 

It will be seen that all the varieties were badly diseased, none of them 
showing promise of being resistant. It is interesting to note however 
that the Triumph, a very early variety, and usually considered to be a 
low yielder as compared with later varieties, gave by far the largest yield, 
in spite of the fact that the tubers were affected. This is believed to 
be on account of its having practically reached maturity at the time 
when the disease became severe. 

The following season forty varieties of potatoes representing nine 
different groups as classified by Stuart (16) were planted on two 
different plots of infested land, one at Arlington and one at East Fish- 
kill, New York, both in Dutchess County. Owing to wet weather it 

TABLE 8 

A test of varietal susceptibility to Fusarium wilt of potato in Dutchess County, 1915. 
Healthy potatoes were planted on infested land 



No. 9 

Triumph 

Rural New Yorker 

Bovee 

Green Mountain. . . 







AMOUNT OP STEM-END 


TOTAL 


WEIGHT 

OF 
15 HILLS 


TOTAL 
TUBERS 


INFECTION 


NUMBER 

OF 
DISEASED 












Bad 


Slight 


None 


TUBERS 


pounds 












12.0 


66 


6 


25 


35 


31 


20.5 


73 


6 


34 


33 


40 


14.5 


48 


12 


22 


14 


34 


4.0 


83 


52 


21 


10 


73 


9.0 


61 


16 


19 


26 


35 



DISEASED 
TUBERS 



per cent 

47 
55 
71 
88 
51 



was not possible to plant before June 12 and June 15, respectively. At 
digging time all of the varieties showed some affection of the tubers. 
All of them were susceptible. Of course there was a large variation in 
the yield of the separate varieties but it was impossible to tell whether 
or not any of the differences were due to resistance. It was observed 
that some of the earlier varieties made a good yield compared with the 
later ones and it is believed that if the planting had been earlier some 
of these would have proved the most satisfactorj^. 



Disease escaping varieties and the date of planting 

It has been noticed that Fusarium wilt does not begin to appear on 
the vines until the middle of the summer when the temperatures are 
the hottest. In the Hudson Valley this is usually from the middle of 



1919] Haskell: Potato Fusarium Wilt 257 

July to the middle of August. At this time early potatoes that have 
been planted early will be approaching maturity while late potatoes 
of the Green Mountain or Rural New Yorker types are just setting tubers. 
The result is that when the vines are dead the yield from the early varie- 
ties will be fairly normal while that from the late potatoes is greatly 
reduced. The case just mentioned of the superior yield of Triumph in 
1915 illustrates this point. On one farm in Dutchess County, for the 
past two seasons, Irish Cobblers, planted early, have yielded 180 bushels 
to the acre as compared with 98 bushels for Green Mountains planted 
later. 

It is a common practice in the Hudson Valley, where potatoes are a 
relatively unimportant crop, to postpone putting in the seed until the 
last of the spring planting. A good crop is sometimes secured in this 
way but too often it happens that the vines are killed early by wilt, when 
the tubers are small. Uniformly better results would be secured by 
planting an early potato like the Irish Cobbler and planting it as early 
as possible in order to mature a crop before the hot weather of the 
middle of August. In Dutchess County the climatic conditions are 
similar to those of some of the early trucking regions further south and 
the potato growing methods carried out there, especially the early plant- 
ing of Irish Cobblers, should be more closely followed. The writer is 
strongly of the opinion that a change in the cultural practice such as 
has just been outlined is probably the most promising and practical 
way of dealing with the Fusarium wilt problem in southeastern New York. 

Summary 

The destructive potato disease of uncertain identity in the southern 
Hudson River Valley has been found to be Fusarium wilt. 

The symptoms of the disease as it occurs in this locality are practi- 
cally the same as described by other writers except that the tubers com- 
monly exhibit a condition in which the vascular system near the stem 
end is browned without the causal organism necessarily being present, 
and which is designated here as "Fusarium necrosis." These potatoes 
are always produced on plants that are affected with Fusarium wilt. 
When they germinate they produce spindling sprouts. 

Isolations and microscopic examination have been made that show 
the fungus to be frequently present in the extreme stem end of tubers 
affected with Fusarium necrosis but entirely absent or very rare in the 
diseased tissue of the interior of such tubers. The pathogene is most 
abundant in the roots, rhizomes and lower parts of the stem. It is not 
commonly present in the upper portions of freshly wilted plants. 



258 Phytopathology [Vol. 9 

That Fusarium oxysporum is the primary cause of the disease, is shown 
by the constant association of the organism with the host, and by the 
artificial production of the disease with the use of pure cultures, sterilized 
seed and sterilized soil. 

Planting experiments, both in Dutchess County and at Ithaca, N. Y., 
show that the pathogene may be communicated, to some extent at least, 
through seed tubers affected with Fusarium necrosis, but on the other 
hand, affected tubers often produce a crop apparently free from Fusarium 
wilt or necrosis. The plants arising from such potatoes however are 
weak and the yield is small so that the use of diseased seed cannot be 
recommended even through the resulting crop may be healthy. 

The soil is the principal source of the inoculum in Dutchess County. 
The disease is most destructive when infection takes place by reason 
of the potatoes being planted in infested land. 

Experiments were conducted in an effort to discover possible reasons 
for a necrosis of the tuber in the absence of any organism. Certain 
toxic solutions, such as 5 per cent oxalic acid, and a liquid extract of 
Fusarium oxysporum, when introduced into the rhizome of the growing 
tuber were found to produce a non-parasitic browning of the potato 
not unlike Fusarium necrosis. A discoloration of the xylem in the stem 
was also produced by killing a portion of the stem with steam, showing 
that the products of decomposing cells have a poisonous effect. It 
seems likely therefore that the apparently non-parasitic affection of the 
tuber accompanying Fusarium wilt may be explained on the basis of 
the presence of toxines. 

The following evidence is given to show that temperature is a very 
important factor in the development of Fusarium wilt. 

1. Fusarium oxysporum makes its best growth at comparatively high 
temperatures (26°-32°C. optimum and 40°C. maximum), while the 
potato plant develops most luxuriously in a relatively cool climate. In 
Dutchess County temperature conditions exist that are favorable for 
the parasite and unfavorable for the host with the result that the disease 
develops to an unusual extent. 

2. The disease appears annually in New York during the hot weather 
of the latter part of July or the first of August. 

3. Within Dutchess County, and also within New York state and 
the United States, the disease is most severe in places where high summer 
temperatures prevail at the time when tuber formation is in progress. 

4. Within Dutchess County there is a distinct correlation between 
the amount of disease and factors influencing soil temperature such as 
altitude, exposure of fields and shading of plants. 



1919] Haskell: Potato Fusarium Wilt 259 

5. Early attempts to produce the disease artificially yielded only 
unsatisfactory, sporadic, or negative results because of failure to recog- 
nize the importance of proper soil temperature. When this was taken 
into account however, and plants were grown at temperatures of 36°C. 
(97°F.) positive results were obtained. 

Soil moisture, soil type and soil fertility while undoubtedly influ- 
encing the disease to some extent are not found to be nearly so important 
in this respect as is soil temperature. 

Crop rotation, under Dutchess County conditions, is of doubtful value 
as a practical means of control. It is recommended as a good cultural 
practice but it does not seem to have any great influence on the amount 
of disease. 

No varietal resistance was noted, and various fertilizers appeared to 
have no influence on the amount of disease. 

The most practical solution of the problem in Dutchess County seems 
to be the planting of early potatoes such as Irish Cobbler very early in 
the season so that the crop is matured before temperature conditions 
are favorable for Fusarium wilt. 

Cornell University, 
Ithaca, New York 

literature cited 

(1) Bouyoucos, G. J.: Soil temperature. Michigan Agr. Expt. Sta. Tech. Bui. 

26: 5-133. 1916. 

(2) Carpenter, C. W.: Some potato tuber-rots caused by species of Fusarium. 

Jour. Agr. Research, 5: 183-210, pi. A-B, 14-19. 1915. Literature cited, 
p. 208-209. 

(3) Dixon, H. H.: Transpiration and the ascent of sap in plants. 216 p., illus. 

London, 1914. 

(4) Jones, L. R., and Oilman, J. C: The control of cabbage yellows through 

disease resistance. Wisconsin Agr. Expt. Sta. Research Bui. 38, 70 p., 
23 fig. 1915. Literature cited, p. 69-70. 

(5) Link, G. K. K.: A physiological study of two strains of Fusarium in 1 lieu- 

causal relation to tuber rot and wilt of potato. Nebraska Agr. Expt. 
Sta. Research Bui. 9, 45 p., illus. 1916. Also published in Bot. Gaz. 
62: 169-209, illus. 1916. 

(6) Manns, T. F.: The Fusarium blight (wilt) and dry rot of the potato. Ohio 

Agr. Expt. Sta. Bui. 229: 299-337, pi. 1-15. 1911. 

(7) Orton, W. A.: The wilt disease of the cowpea and its control. U. S. Dept. 

Agr. Bur. Plant Indus. Bui. 17: 9-22. 1902. 

(8) Orton, W. A.: Cotton wilt. U. S. Dept. Agr. Farmers' Bui. 333, 24 p., illus. 

1908. 

(9) Orton, W. A.: Potato diseases in San Joaquin county, California. U. S. 

Dept. Agr. Bur. Plant Indus. Circ. 23, 14 p. 1909. 
(10) Orton, W. A.: Potato wilt, leaf-roll, and related diseases. U. S. Dept. Agr. 
Bui. 64, 48 p., 16 pi. 1914. Bibliography, p. 44-48. 



260 Phytopathology [Vol. 9 

(11) Overton, J. B.: Studies on the relation of the living cells to transpiration 

and sap-flow in Cyperus. Bot. Gaz., 51: 28-63, fig. 1; 102-120, fig. 2-3. 
1911. 

(12) Rtjmbold, Caroline: Methods of injecting trees. Phytopathology, 5: 225- 

228, pi. 13. 1915. 

(13) Sherbakoff, C. D.: Fusaria of potatoes. New York Cornell Agr. Expt. 

Sta. Mem., 6 : 87-270, 51 fig., 7 col. pi. 1915. Literature cited, p. 269-270. 

(14) Smith, Erwin F., and Swingle, D. B.: The dry rot of potatoes due to Fu- 

sarium oxysporum. U. S. Dept. Agr. Bur. Plant Indus. Bui. 55, 64 p., 
8 pi. 1904. Literature, p. 61-62. 

(15) Stewart, F. C: Another stem blight of potatoes. New York State Agr. 

Expt. Sta. Bui. 101: 83-84. 1896. 

(16) Stewart, F. C: The communicability of stem blight. New York State Agr. 

Expt. Sta. Bui. 138: 632-634. 1897. 

(17) Stuart, William: Group classification and varietal descriptions of some 

American potatoes. U. S. Dept. Agr. Bui. 176, 56 p., 19 pi. 1915. 

(18) Wollenweber, H. W.: Studies on the Fusarium problem. Phytopathology, 

3: 24-50, pi. 5. 1913. 



PLATE XIII 

Fig. A. A plant of the Green Mountain variety affected with Fusarium wilt. 
One stalk is badly diseased and the other only slightly so. 

Fig. B. Two germinating potato tubers from the same source and of the same 
variety. The one on the left is healthy while the one on the right is affected with 
Fusarium necrosis. The difference in the size of the sprouts is very noticeable. 



PHYTOPATHOLOGY IX 



PLATE X1I1 




Fig. A 




Fig. B 
Haskell: Potato Fusarium Wilt 



PLATE XIV 

Fig. A. A diseased plant of the Rural New Yorker type growing beside a com- 
paratively healthy one of the same variety. The color of the stems of ' 'blue- 
sprouts" is usually darker and more intense in wilted plants than in healthy. 

Fig. B. Green Mountain plant, practically dead from Fusarium wilt, that was 
carefully removed from the soil by washing. The photograph shows the effect 
of the disease on the root system and on the yield. 

Fig. C. Aerial tubers produced on stems of affected Green Mountain potato 
plants. This phenomenon frequently occurs after the underground portion of 
the plant has become badly diseased! 

Fig. D. The type of internal browning generally attributed to Fusarium oxyspo- 
rum. Samples from Monroe County. This form of disease is sometimes found in 
the Hudson Valley but the browning does not usually extend inward so deeply as 
in this case and appears more like the condition shown in plate XV. 



PHYTOPATHOLOGY IX 



PLATE XIV 




Haskell: Potato Fusarium Wii 



PLATE XV 

Fig. A. Successive slices across the basal end of a potato affected with Fusarium 
necrosis showing the depth to which the browning extends into the tuber. 

Fig. B. Stem-end browning artificially produced by injecting a five per cent so- 
lution of oxalic acid into the stem below ground. 

Fig. C. Two tubers affected with Fusarium necrosis as it usually appears in 
Dutchess County. 

Fig. D. Old potato tubers from a lot, seventy-five per cent of which were affected 
with Fusarium necrosis, showing progressive stages in the development of a rot 
about the point of attachment of the rhizome. 



PHYTOPATHOLOGY IX 



PLATE XV 










D 



Haskell: Potato Fusarium Wilt 



